In many liquid supply systems, and particularly fuel injection systems for combustion engines, it is desirable to supply liquid fuel to the fuel injectors from a fuel pump which continuously delivers a quantity of liquid fuel sufficient to supply the maximum fuel demand of the engine. Consequently, when the engine is operating under conditions which require less fuel, there is an excess of fuel being delivered from the fuel pump. This is especially true when the engine is idling and has an extremely low fuel demand while the fuel pump is still delivering a large quantity.
In such systems, a bypass pressure regulator is utilized to divert or bypass the excess fuel from the needed supply of fuel consumed by the engine. Preferably, the bypass liquid fuel is diverted back to the liquid supply source such as a fuel tank. In fuel system applications, the fuel pump is typically located inside the fuel tank. The bypass pressure regulator can be located in the tank and immediately downstream of the fuel pump thus diverting bypass fuel directly back into the fuel tank, or it can be located further downstream of the fuel pump and downstream of an injector fuel rail utilized as a manifold which communicates with the injectors. If the bypass pressure regulator is mounted downstream of the fuel injectors, a bypass fuel return line is needed to return the excess fuel back into the fuel tank. Whether the bypass pressure regulator is internal or external to the fuel tank, when utilizing a regulator, the fuel pump can operate continuously maintaining a high rate of fuel output to accommodate a rapidly changing demand for fuel at the engine.
Some previous bypass pressure regulators, such as that disclosed in U.S. Pat. No. 5,727,529, use a flexible diaphragm in a can which is spring biased to close a bypass passage. The diaphragm is responsive to an increase in fuel pressure acting thereon and when displaced, permits the fuel to flow through the bypass passage to be returned to the fuel tank. Although generally satisfactory in performance, and beneficial for the ability to accommodate thermally expanding or excess fuel, these bypass pressure regulators are expensive to manufacture because of the diaphragm and numerous parts. Furthermore, the diaphragm regulators are relatively large, and have a relatively slow response time causing undesirable fuel pressure pulsations which can affect the performance of the engine and can generate undesirable levels of noise in the fuel system or other liquid systems.
Other bypass pressure regulators, such as that disclosed in U.S. Pat. No. 5,975,061 and incorporated herein by reference, do not utilize a diaphragm. As best illustrated in FIG. 1, marked prior art, the bypass pressure regulator 20 typically has a valve body 22 defining a bypass passage 24 having an inlet 26 in communication with a fuel pump (not shown) and an outlet 28 in communication with a fuel tank (not shown). A valve assembly 30 is received in and controls the flow of fuel through the bypass passage 24. The valve assembly 30 is composed of many difficult to manufacture and assemble parts including an enlarged, disc-like valve head 32 attached concentrically to a valve shank 34 at one end and attached to a disc 36 at an opposite end. A spring 38 biases the regulator closed, and is compressed axially between the disc 36 and a radially inward projecting shoulder 40 of the valve body 22 through which the shank 34 projects in an upstream direction. A valve seat 42 carried by the body 22 faces generally downstream with respect to the bypass fuel flow (identified by arrow 44) and a resilient annular ring 46 attached to the enlarged head 32 releasably seals to the seat 42 when the regulator 20 is closed. So as not to obstruct bypass fuel flow 44 through the passage 24 and to expose the valve head 32 to the acting fuel pressure, numerous orifices 48 are formed in the disc 36 and shoulder 40 of the valve body 22 lending toward additional manufacturing costs and complexities.
Furthermore and unfortunately, known bypass pressure regulators like regulator 20 do not maintain a constant pressure drop through the valve under varying flow rates. In operation, the spring force and generally the area of the exposed head 32 determine the fuel pressure at which the valve will “crack” or begin to open. When the valve assembly 30 first starts to open, flow through the annulus between the valve head 32 and seat 42 develops at high velocities relative to the surrounding fuel. This high velocity produces a low pressure region 50 exerting a force on the valve assembly 30 which is additive to the spring force and thus tends to close the valve assembly 30. In known bypass pressure regulators this low pressure region can lead to unstable oscillations of the valve assembly 30, fuel pressure flow rate fluctuations and noise of the valve assembly. In extreme cases, the regulator can be damaged by the hammering effect of the components. Yet further, known bypass pressure regulators are not easily integrated into other components of a typical fuel system or pump module of a combustion engine, are relatively complex, and relatively expensive to manufacture.